Chief spokesman Dan Stessel said Metro “cannot decline ads based on political content.”

Stessel wrote in an e-mail that Metro’s advertising “has been ruled by the courts as a public forum protected by the First Amendment.”

“WMATA does not endorse the advertising on our system, and ads do not reflect the position of the Authority,” he wrote, referring to the Washington Metropolitan Area Transit Authority.

It was unclear when the ad was posted. CBS Outdoor, which handles advertising for the transit system, would not comment on the ad. Logan Clements, a film producer in Los Angeles and executive producer of “Free Star Movie,” a film about what he envisions health care to be under Obama’s plan, said he put the ad up at the Clarendon station because “that’s where I could afford to put it.”

He spent $800 for the ad to run from mid-February to mid-March. “I wanted to call attention to where Obamacare is going take American medicine,” he said. “The point of the ad is to express the degree of outrage. They’re going to take a sick system and make it sicker.”

Rep. James P. Moran (D-Va.) wrote to Metro on Wednesday, asking that the ad be removed and calling it “an offensive advertisement disparaging the recent health law.”

“This advertisement is inappropriate, disrespectful of the President, and should be removed immediately,” Moran said in a statement on his Web site. “The families with children and thousands of tourists who take Metro everyday should not be subjected to such garbage. I understand WMATA vets these advertisements before allowing them to go up, but it seems someone wasn’t doing their job when this ad was approved.”

Moran later expressed dismay at Metro’s decision not to remove the ad.

“I am disappointed by WMATA’s defense of this inappropriate advertisement,” he said in a news release. “If their current advertising guidelines do not prohibit profane advertisements on taxpayer-funded property, then WMATA should take the initiative and update them. Profanity has no place in the public forum.”